The new cultivar is a product of a planned breeding program. This new variety, hereinafter referred to as ‘HOLDEN52’, was discovered as a seedling, resulting from the crossing of an unpatented, unnamed Rhododendron hyperthyrum with the pollen parent Rhododendron hybrida ‘Henry's Red’, unpatented. The cross resulting in the new variety occurred during 2005. The new variety was selected by the inventor during of 2010 at an arboretum in Madison, Ohio.
After identifying the new variety as a potentially interesting selection, the inventor first organized propagation of ‘HOLDEN52’ by vegetative cuttings Fall of 2007 at the same arboretum in Madison, Ohio. The inventor continued controlled testing and propagation, assessing stability of the unique characteristics of this variety. Multiple generations have been reproduced and have shown that the unique features of this cultivar are stable and reproduced true to type.